Nitric oxide (NO) has emerged as a novel regulator of several ovarian
events, such as ovulation, steroidogenesis, and apoptotic cell death. The
NO synthases (NOS) are a family of enzymes that catalyze the oxidation of
L-arginine to NO and L-citrulline. Three main isozymes exist in mammals that are regulated by distinct genes: a constitutive neuronal NOS (nNOS or NOS1), an endotoxin- and cytokine-inducible NOS (iNOS or NOS2), and a constitutive endothelial NOS (eNOS or NOS3) (Stuehr et al. 2001).
NCBI Summary:
Nitric oxide is a reactive free radical which acts as a biologic mediator in several processes, including neurotransmission and antimicrobial and antitumoral activities. This gene encodes a nitric oxide synthase which is expressed in liver and is inducible by a combination of lipopolysaccharide and certain cytokines. Three related pseudogenes are located within the Smith-Magenis syndrome region on chromosome 17. [provided by RefSeq, Jul 2008]
General function
Enzyme
Comment
Cellular localization
Cytoplasmic
Comment
In control ovaries, eNOS was detected in the theca cell layer, ovarian
stroma, and on the surface of oocytes. During follicular development, eNOS
staining was still expressed in the theca cell layer and was also present in
mural granulosa cells. After ovulation, homogenous eNOS staining was
observed within cells of the corpus luteum (CL) (Jablonka-Shariff, et al., 1997).
Nitric Oxide Synthase Is Involved in Follicular Development via the PI3K/AKT/FoxO3a Pathway in Neonatal and Immature Rats. Li J et al. (2020) It is assumed that nitric oxide synthase and nitric oxide are involved in the regulation of female reproduction. This study aimed to assess the roles of nitric oxide synthase (NOS) in follicular development. The endothelial NOS (eNOS) inhibitor L-NAME, inducible NOS (iNOS) inhibitor S-Methylisothiourea (SMT) and NOS substrate L-arginine (L-Arg) were used in the NOS inhibition models in vivo. Neonatal female rats were treated with phosphate buffer saline (PBS, control), L-NAME (L-NG-Nitroarginine Methyl Ester, 40 mg/kg), SMT (S-Methylisothiourea, 10 mg/kg), L-NAME + SMT, or L-Arg (L-arginine, 50 mg/kg) via subcutaneous (SC) injection on a daily basis for 19 consecutive days, with the samples being collected on specific postnatal days (PD5, PD10, and PD19). The results indicated that the number of antral follicles, the activity of total-NOS, iNOS, neuronal NOS (nNOS), and eNOS, and the content of NO in the ovary were significantly (p < 0.05) increased in the L-Arg group at PD19, while those in L + S group were significantly (p < 0.05) decreased. Meanwhile, the ovarian expression in the L-Arg group in terms of p-AKT, p-FoxO3a, and LC3-II on PD19 were significantly (p < 0.05) upregulated, while the expressions of PTEN and cleaved Caspase-3 were (p < 0.05) downregulated as a result of NOS/NO generation, respectively. Therefore, the results suggest that NOS is possibly involved in the maturation of follicular development to puberty via the PI3K/ AKT/FoxO3a pathway, through follicular autophagia and apoptosis mechanisms.//////////////////
Nitric oxide synthase isoforms and the effect of their inhibition on meiotic maturation of porcine oocytes. Chmel?v? et al. SummaryIn this paper we assessed: (i) the change in nitric oxide synthase (NOS) isoforms' expression and intracellular localization and in NOS mRNA in porcine oocytes during meiotic maturation; (ii) the effect of NOS inhibition by Nomega-nitro-l-arginine methyl ester (l-NAME) and aminoguanidine (AG) on meiotic maturation of cumulus-oocyte complexes (COC) as well as denuded oocytes (DO); and (iii) nitric oxide (NO) formation in COC. All three NOS isoforms (eNOS, iNOS and nNOS) and NOS mRNA (eNOS mRNA, iNOS mRNA and nNOS mRNA) were found in both porcine oocytes and their cumulus cells except for nNOS mRNA, which was not detected in the cumulus cells. NOS isoforms differed in their intracellular localization in the oocyte: while iNOS protein was dispersed in the oocyte cytoplasm, nNOS was localized in the oocyte cytoplasm and in germinal vesicles (GV) and eNOS was present in dots in the cytoplasm, GV and was associated with meiotic spindles. l-NAME inhibitor significantly suppressed metaphase (M)I to MII transition (5.0 mM experimental group: 34.9% MI, control group: 9.5% MI) and at the highest concentration (10.0 mM) also affected GV breakdown (GVBD); in contrast also AG inhibited primarily GVBD. The majority of the oocytes (10.0 mM experimental group: 60.8%, control group: 1.2%) was not able to resume meiosis. AG significantly inhibited GVBD in DO, but l-NAME had no significant effect on the GVBD of these cells. During meiotic maturation, NO is formed in COC and the NO formed by cumulus cells is necessary for the process of GVBD.
Jablonka-Shariff, et al. (1998)reported results that support a role for NO in the ovulatory process. The ovarian defects observed in the eNOS knock-out mice suggest that eNOS-derived NO is a modulator of oocyte meiotic maturation.
Jablonka-Shariff et al. (1999) observed that significantly fewer ovulated oocytes obtained from rats treated with NOS inhibitors were at metaphase II (P < .006), the normal stage of meiosis for unfertilized oocytes, and a significantly greater percentage of oocytes displayed atypical morphology
as compared with control oocytes (P < .0001). Jablonka, et al. (1999)
concluded that ovarian nitric oxide synthesis is required for maximal ovulation, and a lack of nitric oxide during the periovulatory period results in severe defects in oocyte maturation.
Olson et al. (1996) suggested that nitric oxide participates in functional luteal regression by inhibiting steroidogenesis.
Gobbettic et al. (1999) showed that nitric oxide synthase acutely regulates progesterone production by in vitro cultured rabbit corpora lutea.
In the study of the possible role of nitric oxide regulating ovarian
steroidogenesis, Motta et al. (1997) found that L-NMMA increased progesterone production and diminished prostaglandin F2 alpha synthesis
in ovarian tissue from pseudopregnant rats in the late phase. These results
suggest that nitric oxide could participate in the corpus luteum demise in
the rat by modulating part of prostaglandin F2 alpha and progesterone
production.
In addition, Yamauchi et al. (1997) concluded that the ovarian NO/NOS system is involved in follicle rupture during the ovulatory process. NO may induce follicle rupture in rabbit ovaries at least in part by the stimulation of
prostaglandin production.
Matsumi H, et al. (1998) reported an inverse relationship between apoptosis and inducible nitric oxide synthase expression in rat granulosa cells and suggested a possible role of nitric oxide in ovarian follicle atresia.
Expression regulated by
Comment
Motta, et al. (1997) found that nitric oxide synthase activity diminishes with the corpus luteum development.
Ovarian localization
Oocyte, Cumulus, Granulosa, Theca, Luteal cells
Comment
Direct real-time measurement of intra-oocyte nitric oxide concentration in vivo. Goud PT 2014 et al.
Nitric oxide (NO) is reported to play significant a role in oocyte activation and maturation, implantation, and early embryonic development. Previously we have shown that NO forms an important component of the oocyte microenvironment, and functions effectively to delay oocyte aging. Thus, precise information about intra-oocyte NO concentrations NO] will result in designing more accurate treatment plans in assisted reproduction. In this work, the direct, real-time and quantitative intra-oocyte [NO] was measured utilizing an L-shaped amperometric integrated NO-selective electrode. This method not only provides an elegant and convenient approach to real-time the measurement of NO in physiological environments, but also mimics the loss of NO caused by rapid NO diffusion combined with its reactivity in the biological milieu. This experiment suggests that the NO levels of oocytes obtained from young animals are significantly higher than those of oocytes obtained from old animals. Additionally the NO levels stay constant during the measurements; however, the intra-oocyte [NO] is reduced significantly (70-75% reduction) in response to L-NAME incubation, suggesting that NO measurements are truly NOS based rather than caused by an unknown interfering substance in our system. We believe this first demonstration of the direct quantitative measurement of [NO] in situ in an intact cellular complex should be useful in tracking real-time and rapid changes at nanomolar levels. Moreover, this finding confirms and extends our previous work showing that supplementation with NO delays the oocyte aging process.
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Inducible Nitric Oxide Synthase and Heme Oxygenase 1 Are Expressed in Human Cumulus Cells and May Be Used as Biomarkers of Oocyte Competence. [Loredana B 2014 et al.
The interplay between oocyte and surrounding cumulus cells (CCs) during follicular growth influences oocyte competence to undergo fertilization and sustain embryo development. The expression of many genes and proteins in CCs has been suggested as potential biomarker of oocyte competence in human in vitro fertilization (IVF). In the present study, we analyzed 90 human cumulus-oocyte complexes obtained during IVF procedure: 30 CCs were analyzed using quantitative real-time polymerase chain reaction and 60 CCs using Western blotting analysis to detect gene and protein expression of some enzymes related to oxidative stress, that is, the 3 nitric oxide synthase (NOS) isoforms and heme oxygenase 1 (HO-1). In the group of 60 CCs, we also investigated the expression and phosphorylation of IkBa, a known inhibitor of the nuclear factor ?B (NF-?B) pathway, which controls several redox-sensitive genes. The expression of the messenger RNAs (mRNAs) was related to the oocyte morphological analysis performed by polarized light microscopy and to the occurrence of normal fertilization after intracytoplasmic sperm injection. We observed that the amount of iNOS and HO-1 mRNAs and proteins is significantly higher, and that in the meanwhile the NF-?B pathway is activated, in CCs corresponding to oocytes that were not fertilized in comparison to CCs whose corresponding oocyte showed normal fertilization. Instead, no correlation between the fertilization and the oocytes' morphological data was observed. These results suggest that the increase in iNOS and HO-1 mRNAs expression in CCs is a negative index of oocyte fertilizability and might be an useful tool for oocyte selection.
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In immature ovaries and during follicular development, iNOS staining was
found within the theca cell layer and stroma. After ovulation, NOS staining
was present only in the external layers of the developing CL, but in the
degenerating corpus luteum (10 days post-hCG), strong staining in nonparenchymal
cells was observed within the entire corpus luteum.
Huo LJ, et al reported that inducible nitric oxide synthase-derived nitric oxide regulates germinal vesicle breakdown and first polar body emission in the mouse oocyte.
The present study investigated the subcellular localization of inducible nitric oxide synthase (iNOS) during mouse oocyte meiotic maturation and fertilization using confocal microscopy, and further studied the roles of iNOS-derived NO in oocyte maturation by using an iNOS-specific inhibitor aminoguanidine (AG) and iNOS antibody microinjection. In germinal vesicle-stage oocytes, iNOS immunoreactivity was mainly localized in the germinal vesicle. Shortly after germinal vesicle breakdown, the iNOS immunoreactivity accumulated around the condensed chromosomes. At metaphase I and metaphase II, with the organization of chromosomes to the equatorial plate, iNOS immunoreactivity was concentrated around the aligned chromosomes, putatively the position of the metaphase spindle. The accumulation of iNOS immunoreactivity could not be detected at anaphase I and anaphase II. However, at telophase I and telophase II, the staining of iNOS was concentrated in the region between the separating chromosomes/chromatids. Furthermore, the staining of iNOS also accumulated in the male and female pronuclei in fertilized eggs. Germinal vesicle breakdown and the first polar body emission of the oocytes were significantly blocked by the iNOS-specific inhibitor AG in a dose-dependent manner. The germinal vesicle breakdown in oocytes injected with iNOS antibody was also inhibited. We found that the phosphorylation of mitogen-activated protein kinase in oocytes after germinal vesicle breakdown was inhibited by AG treatment. The control oocytes extruded a normal first polar body, while the AG-treated oocytes exhibited an elongated protrusion or no elongated protrusion. The results of confocal microscopy showed that the AG-treated oocytes were arrested at anaphase I-telophase I. Our results suggest that the iNOS-derived NO pathway plays important roles in mouse oocyte meiotic maturation, especially in germinal vesicle breakdown and the anaphase-telophase transition.
Follicle stages
Preovulatory, Corpus luteum
Comment
Phenotypes
Mutations
1 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: None Comment:Jablonka-Shariff et al. (1999) studied the roles of nitric oxide (NO) and nitric oxide synthase (NOS) in reproduction were studied by examining the estrous cycle of wild-type (WT) mice, inducible NOS (iNOS)-, and endothelial NOS (eNOS)-knockout mice. They observed an average estrous cycle of 4.8 +/- 0.2 days in WT mice. While we observed no significant influence of iNOS deficiency on cycle length, eNOS-knockout females showed a significantly longer estrous cycle (6.6 +/- 0.6 days; p < 0.03) than WT females, due to an extension of diestrus (p < 0.03). There was no influence of iNOS deficiency on ovulation rate compared with that in WT females; however, eNOS-knockout mice showed a significant reduction (p < 0.05) in ovulatory efficiency relative to WT or iNOS-knockout females. In contrast to WT females, in which the highest level of estradiol (E2) was observed at 1500 h of proestrus, iNOS-knockout females reached a peak of E2 at 1830 h of proestrus. In eNOS-knockout females, the peak of E2 occurred at 1830 h, as in iNOS-knockout mice; however, E2 levels were 5-fold and 3-fold higher (p < 0.05) than levels observed in WT and iNOS-knockout females, respectively. There was no effect of genotype on the plasma LH concentrations at proestrus. On the first day of diestrus, eNOS-knockout females showed significantly higher plasma E2 and progesterone levels (p < 0.05) relative to WT and iNOS-knockout females. The dysfunction in cyclicity, ovulation rate, ovarian morphology, and steroidogenesis in eNOS-knockout female mice strongly supports the concept that eNOS/NO plays critical roles in ovulation and follicular development.